Chronic cocaine use causes brain abnormalities and cognitive dysfunction, which may both impair a drug user's ability to resist further drug use and decrease the efficacy of treatment interventions. The severity of cocaine associated brain dysfunction is less in women than in men. Further, cocaine abuse treatment appears to benefit women more than men. These sex differences have important therapeutic implications, because they suggest a protective role for estrogen. Thus, estrogen (or a related compound) might be of therapeutic use to protect against brain vascular dysfunction. Cocaine's ability to reduce cerebral blood flow is likely to play a critical role in the development of brain dysfunction. Estrogen has been shown to acutely improve, while progesterone and testosterone acutely degrade vascular function. Consequently, vascular effects of hormones may account for sex differences in cocaine's brain effects. We seek to determine whether estrogen, progesterone, and testosterone alter cocaine pharmacokinetics and cocaine's acute cerebral vasoconstrictive effects. We will measure cocaine and hormone pharmacokinetics, and characterize cardiovascular responses after combined intravenous cocaine (0.4 mg/kg) and estrogen (men), or progesterone or testosterone (women) treatments. Subsequently, we will evaluate whether these hormones alter cocaine's acute cerebrovascular effects, using a noninvasive functional MRI technique called Dynamic Susceptibility Contrast MRI (DSC MRI). DSC MRI measures cerebral blood volume (CBV) and blood flow (CBF). Study subjects will include healthy men and women with histories of occasional cocaine use, who will each participate in a randomized, placebo-controlled, double-blind study. The pharmaceutical industry is actively developing novel steroid receptor agents with greater receptor selectivity than the natural hormones, which may improve the ability to selectively modulate vascular responses to cocaine. Thus, if our hypotheses regarding hormonal effects on cocaine-induced vasoconstriction are validated, the potential for identifying effective therapeutics for investigation in chronic treatment trials will be enhanced.